The present invention relates to a method and an apparatus for airtightly packaging a semiconductor package, and more particularly to a method and an apparatus for airtight packaging of a semiconductor package suitable for solder sealing a multi-chip module having a large number of LSI chips mounted on a ceramic substrate.
A semiconductor package is formed by attaching a cap to a substrate such as a ceramic substrate having semiconductor devices mounted thereon by solder and by sealing them, with the semiconductor devices being airtightly packaged in a space formed by the substrate and the cap.
Airtight solder packaging for a multi-chip module having semiconductor devices mounted on a ceramic substrate is conducted in a hermetically sealed receptacle as described in, for example, Japanese Patent Unexamined Publication Nos. 5570/78 and 20860/78 (JP-A-53-5570 and JP-A-53-20860). As disclosed in these publications, the difference in temperature and pressure between the inside and outside of the module caused during the solidification process of solder is eliminated in order to prevent a short circuit or the like due to a projection of solder in the space within the package. In methods described in Japanese Patent Unexamined Publication Nos. 148445/80 and 22493/77 (JP-A-55-148445 and JP-A-52-22493), metal for absorbing the surplus solder is disposed at a minute interval on the internal periphery of the metal portion whereto solder is to be attached. In a method disclosed in Japanese Patent Unexamined Publication No. 7172/78 (JP-A-53-7172), a groove for stopping the surplus solder is provided instead of the metal for absorbing the surplus solder. In the above-described publications, it is assumed that the weight of either the cap or the substrate (wiring substrate) is smaller than the surface tension of the solder for airtight packaging. If the weight of the cap or the wiring substrate is increased due to, for example, a large-sized package the packaging solder is crushed and scattered inside and outside the package when it is melted. As a result, the desired amount of solder may not be ensured or an electrical short circuit may be caused. It is necessary to ensure a sufficient amount of sealing solder for the purpose of absorbing the thermal strain as a buffer when there is a difference in thermal expansion between the cap and the wiring substrate and for the purpose of reliable soldering. From this point of view, a method for packaging the heavy cap and the wiring substrate by solder has been demanded.